1. Field of the Invention
The present invention relates to a process for determining the presence or absence of a possibility that a vehicle is overturning laterally or sideways, based on a rolling angle and a rolling angular speed of the vehicle, and to a system for detecting an angle of inclination of the vehicle.
2. Description of the Related Art
A process for determining a possibility of lateral overturning of a vehicle is known from Japanese Patent Application Laid-open No.7-164985. In this known process, a lateral overturning region is established on a two-dimensional map made using a rolling angle and a rolling angular speed as parameters in an area where the rolling angle and the rolling angular speed are large (an area spaced apart from an origin), and a lateral non-overturning region is established on the map in an area where the rolling angle and the rolling angular speed are small (an area including the origin). When a hysteresis line made by plotting actual rolling angles and actual rolling angular speeds, detected respectively by sensors, on the map enters the lateral overturning region from the lateral non-overturning region, it is determined that there is a possibility that the vehicle is overturning laterally or sideways, whereby an active roll bar is raised.
Principal parameters governing the presence or absence of a possibility that the vehicle is overturning laterally or sideways, are the rolling angle and the rolling angular speed, and in addition to these, there are parameters promoting or inhibiting the lateral overturning of the vehicle. For example, even if the rolling angle and the rolling angular speed of the vehicle are of the same level, the degree of the possibility of the lateral overturning is varied largely depending on a lateral acceleration of the vehicle. More specifically, if a lateral acceleration is generated in a direction of inclination of the vehicle, the lateral overturning of the vehicle is promoted. And if a lateral acceleration is generated opposite to the direction of inclination of the vehicle, the lateral overturning of the vehicle is inhibited. In addition, even if the rolling angle and the rolling angular speed of the vehicle are of the same level, the degree of the possibility of the lateral overturning is varied largely depending on a lateral slipping of the vehicle. More specifically, when the vehicle has been slipped laterally in a direction of rolling of the vehicle, whereby a tire has collided against an obstacle such as a curb, a large rolling moment about the curb is generated to promote the lateral overturning of the vehicle.
When a steering wheel is operated leftwards, the vehicle is inclined rightwards. When the steering wheel is operated rightwards, the vehicle is inclined leftwards. Therefore, when a lateral lane change is conducted continuously, or when the vehicle travels through an S-shaped road, the vehicle is inclined alternately leftwards and rightwards. When the frequency of the operation of the steering wheel is closer to the frequency of an inherent vibration of a suspension provided on the vehicle, there is a possibility that the rolling angle of the vehicle may be liable to be diverged due to a resonance, resulting in the lateral overturning.
In addition, even if the rolling angle and the rolling angular speed of the vehicle are of the same level, the degree of the possibility of the lateral overturning is varied largely depending on a steering angle of the vehicle. More specifically, when the steering wheel is operated leftwards, the vehicle is rolled rightwards. When the steering wheel is operated rightwards, the vehicle is rolled leftwards. Therefore, when the steering wheel is operated leftwards in a state in which the vehicle has been rolled rightwards, the rightward overturning of the vehicle is promoted. When the steering wheel is operated rightwards in a state in which the vehicle has been rolled leftwards, the leftward overturning of the vehicle is promoted.
Further, even if the rolling angle and the rolling angular speed of the vehicle are of the same level, the degree of the possibility of the lateral overturning is varied largely depending on a rolling angular acceleration of the vehicle. More specifically, when a rolling angular speed has been generated in a direction to increase the absolute value of a rolling angle of the vehicle, the lateral overturning of the vehicle is promoted if a rolling angular acceleration is generated in a direction to increase the absolute value of the rolling angular speed. On the other hand, if a rolling angular acceleration is generated in a direction to decrease the absolute value of the rolling angular speed, the lateral overturning of the vehicle is inhibited.
In the process described in Japanese Patent Application Laid-open No.7-164985, a rolling angle xcex8 of the vehicle is detected using two sensors. The first sensor is a sensor for detecting an inclination angle with respect to the direction of gravity force, and detects an initial value xcex80 of a rolling angle of the vehicle based on a component of a gravitational acceleration in a lateral direction of a vehicle body and a component of the gravitational acceleration in a vertical direction of the vehicle body when an ignition switch is turned ON. The second sensor calculates an amount of change in rolling angle according to ∫xcfx89dt by time-integrating a rolling angular speed xcfx89 of the vehicle. The rolling angle xcex8 of the vehicle is given as a sum of outputs from the two sensors according to xcex8=xcex80+∫xcfx89dt.
It is surely possible to detect the rolling angle xcex8 of the vehicle, even if using the first sensor alone. However, a lateral acceleration generated with the turning movement of the vehicle and a vertical acceleration generated due to unevenness of a road surface cannot be recognized as components of the gravitational acceleration in lateral and vertical directions of the vehicle body, respectively. For this reason, there is a possibility that a large error may be generated in the detection of a rolling angle xcex8 during traveling of the vehicle. Moreover, there is a problem that a rolling angle xcex8 cannot be detected during free dropping of the vehicle.
The second sensor detects an amount of change in rolling angle xcex8 by time-integrating a rolling angular speed xcfx89 and hence, it is necessary to use another sensor for detecting an initial value xcex80 of rolling angle xcex8 in combination with the second sensor, as described in Japanese Patent Application Laid-open No.7-164985. Moreover, the rolling angular speed sensor suffers from the following problem. It is difficult to avoid the generation of a drift, and even in a state in which the rolling angular speed xcfx89 is 0, the output does not necessarily assume 0. For this reason, an error is liable to be generated in the amount of change in rolling angle xcex8, which is an integration value of such output.
Accordingly, it is a first object of the present invention to ensure that, when it is determined whether there is a possibility that a vehicle is overturning laterally or sideways, based on a rolling angle and a rolling angular speed of the vehicle, the accuracy of the determination is further enhanced.
It is a second object of the present invention to provide an inclination angle detecting system capable of accurately detecting an angle of inclination of a vehicle in various situations.
To achieve the above first object, according to a first aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the steps of: establishing a threshold value line on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, plotting a hysteresis line for an actual rolling angle and an actual rolling angular speed on the two-dimensional map, and determining that there is a possibility that the vehicle is overturning laterally or sideways when the hysteresis line traverses the threshold value line from a side nearer to an origin of the map to a side farther from the origin, the threshold value line being changed depending on a lateral acceleration of the vehicle.
With the above process, the threshold value line established on the two-dimensional map made with the rolling angle and the rolling angular speed of the vehicle used as parameters is changed depending on the lateral acceleration of the vehicle. Therefore, it is possible to compensate for a variation in possibility of lateral overturning of the vehicle depending on the lateral acceleration of the vehicle to achieve a further accurate determination.
To achieve the first object, according to a second aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the steps of: establishing a threshold value line on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, plotting a hysteresis line for an actual rolling angle and an actual rolling angular speed on the two-dimensional map, and determining that there is a possibility that the vehicle is overturning laterally or sideways when the hysteresis line traverses the threshold value line from a side nearer to an origin of the map to a side farther from the origin, the threshold value line being changed depending on a lateral speed of the vehicle.
With the above process, the threshold value line established on the two-dimensional map made with the rolling angle and the rolling angular speed of the vehicle used as parameters is changed depending on the lateral speed of the vehicle. Therefore, it is possible to compensate for a variation in the possibility of lateral overturning of the vehicle depending on the lateral speed of the vehicle to achieve a further accurate determination.
To achieve the first object, according to a third aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the steps of: establishing a threshold value line on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, plotting a hysteresis line for an actual rolling angle and an actual rolling angular speed on the two-dimensional map, and determining that there is a possibility that the vehicle is overturning laterally or sideways when the hysteresis line traverses the threshold value line from a side nearer to an origin of the map to a side farther from the origin, the two-dimensional map including four quadrants in which the positive and negative signs of the rolling angle and the positive and negative signs of the rolling angular speed are combined with one another, whereby when the hysteresis line extends astride at least three of the quadrants and the distance of the hysteresis line from the origin is increased, the threshold value line is moved toward the origin.
With the above process, when the hysteresis line extends astride the at least three quadrants and the distance of the hysteresis line from the origin is increased, the threshold value line is moved toward the origin. Therefore, when the rolling angle of the vehicle is diverged due to a resonance, resulting in a state in which the vehicle is liable to overturn laterally or sideways, it is much more likely possible that the hysteresis line traverses the moved threshold value line from the side nearer to the origin to the side farther from the origin, thereby early determining that there is a possibility that the vehicle is overturning laterally or sideways.
To achieve the first object, according to a fourth aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the steps of: establishing a threshold value line on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, plotting a hysteresis line for an actual rolling angle and an actual rolling angular speed on the two-dimensional map, and determining that there is a possibility that the vehicle is overturning laterally or sideways when the hysteresis line traverses the threshold value line from a side nearer to an origin of the map to a side farther from the origin, the threshold value line being changed depending on a direction of change in steering angle of the vehicle.
With the above process, the threshold value line established on the two-dimensional map made using the rolling angle and the rolling angular speed of the vehicle as parameters is changed depending on the direction of change in steering angle of the vehicle. Therefore, it is possible to compensate for a variation in the possibility of lateral overturning of the vehicle depending on the direction of change in steering angle of the vehicle, to achieve a further accurate determination.
To achieve the first object, according to a fifth aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the steps of: establishing a threshold value line on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, plotting a hysteresis line for an actual rolling angle and an actual rolling angular speed on the two-dimensional map, and determining that there is a possibility that the vehicle is overturning laterally or sideways when the hystersis line traverses the threshold value line from a side nearer to an origin of the map to a side farther from the origin, the threshold value line being changed depending on a rolling angular acceleration of the vehicle.
With the above process, the threshold value line established on the two-dimensional map made using the rolling angle and the rolling angular speed of the vehicle as parameters is changed depending on the rolling angular acceleration of the vehicle. Therefore, it is possible to compensate for a variation in possibility of lateral overturning of the vehicle depending on the rolling angular acceleration of the vehicle, to achieve a further accurate determination.
To achieve the second object, according to a sixth aspect and feature of the present invention, there is provided a system for detecting an angle of inclination of a vehicle, comprising: a first detecting means for continuously detecting an angle of inclination of the vehicle with respect to a direction of the force of gravity; a second detecting means for continuously detecting an amount of change in angle of inclination of the vehicle by integrating the angular speed of the vehicle; and an adding means for adding a first output from the first detecting means and a second output from the second detecting means to calculate an angle of inclination of the vehicle.
With the above arrangement, the output from the first detecting means for continuously detecting the angle of inclination of the vehicle with respect to the direction of the force of gravity and the output from the second detecting means for continuously detecting the amount of change in angle of inclination of the vehicle by integrating the angular speed of the vehicle are added to each other in the adding means to calculate the angle of inclination of the vehicle. Therefore, even if an error is generated in one of the outputs from the first and second detecting means, the influence of such error can be alleviated by the other accurate output, thereby enhancing the accuracy of the detection of the inclination angle of the vehicle.
The above and other objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.